1. Field of the Invention
The present invention relates to a solid-state radiation detecting device that uses a CCD (charge coupled device) or a BBD (bucket brigade device) and is suitable for detecting a two-dimensional image of high-energy radiation such as X rays, rays, or charge particles.
2. Description of the Related Art
In the fields of astronomy and medical treatment, it is necessary to two-dimensionally detect, i.e., obtain a two-dimensional image of, X rays or the like by converting those into an electrical signal. For this purpose, a solid-state detecting device that is strong and capable of miniaturization is desired.
To this end, as described in detail in, for instance, the Journal of The Physical Society of Japan, Vol. 48, No. 4, pp. 264-270, 1993, it has been attempted to use a high-resistivity substrate and make the depletion layer thicker in a solid-state imaging device using a CCD that was developed as a solid-state imaging device for visible light. With this method, quantum efficiency of about 50% has been obtained at 10 keV.
Another approach is known in which a scintillator layer for converting x rays or the like into visible light is provided on the surface of a solid-state imaging device.
For example, a solid-state radiation detecting device using a CTD (charge transfer device) that is used for the above purpose is configured as shown in FIG. 2, which shows the basic configuration of an interline CTD. Charge that is generated by a 1-pixel photoelectric conversion element 13 is moved to a vertical transfer CTD 21 via a transfer gate 23 and then moved to a horizontal CTD 22. An output signal is obtained from an output gate 24.
As shown in the sectional view of FIG. 9, a 1-pixel structure includes, in addition to the photoelectric conversion element 13, a CTD 14 that is a vertical transfer CCD in this case. In this example, the photoelectric conversion element 13 is a photodiode and the vertical transfer CCD is a buried-channel CCD (BCCD).
In the above solid-state radiation detecting device, the detection efficiency of high-energy radiation is low because the depletion layer cannot be made sufficiently long. Further, radiation damage easily occurs because the MOS structure such as a CCD is used at many locations in signal processing circuits mainly for a scanning function. In addition, since the photoelectric conversion elements and the signal processing circuits are formed on the same surface, the effective area of the detecting section is limited.
In the case of using a scintillator, the resolution is sacrificed and the detection efficiency of low-energy radiation is low. Further, it is difficult to form an optically superior scintillator layer on a solid-state imaging device.